Robert De Niro learned to play the saxophone (in three months) in order to make his performance look more authentic. Unfortunately, his sax playing still had to be overdubbed and it is veteran jazz musician George Auld who does the playing and also plays a band leader.
Steven Prince directed a scene himself when Martin Scorsese walked off the set after a dispute with Robert De Niro.
The original song titled "Theme from New York, New York" was scrapped at the insistence of Robert De Niro. Grudgingly, John Kander and Fred Ebb wrote a new version, which has since become one of the most famous and often recorded songs in history. Kander and Ebb have often expressed extreme gratitude to De Niro for his influence.
Liza Minnelli and Martin Scorsese have said that virtually all of the dialogue in the film was improvised. This created later difficulty during editing, as Scorsese and the editors struggled to create a streamlined narrative.
The blonde woman observed by Robert De Niro dancing with the sailor under the subway tracks at night is Liza Minnelli in a wig.